1. Start with a clear glass jar, as large as you like. I use a recycled one gallon (that's about 4 liters) jar. Fill it with cold water.
2. Add tea bags of your favorite tea. I like Stash teas (that's a brand name in the USA; I don't know if it's available elsewhere). They come in many flavors, both with and without caffeine. Each bag is good for 2 cups of tea, so I use 8 bags in a gallon. If you prefer loose tea, I'm sure it will work, also, but you will need to experiment with amounts.
(If you click on the second picture you will see the swirls of color from the tea infusing into the water.)
5. Enjoy!
Hints:
This can be done without the sun on your kitchen counter, but then it won't be SUN tea! :))
The tea can be frozen into cubes to add to the glasses so it isn't diluted when you drink it.
I store what is not consumed right away in the refrigerator for future thirst.